Many exercises for therapy, sports, recreation or body-building involve the use of free weights. Free weights are held in the hand and moved along predetermined trajectories to exercise specific muscle groups. The motion is repeated for a specific number of times. However, it is difficult to precisely follow a predetermined trajectory for each repetition. It is also difficult to maintain a smooth and controlled motion. Abrupt loss of control may injure muscles. In certain strenuous exercises involving relatively heavy free weights, the repeated motion and weight can impact muscle groups other than those intended to be exercised, leading to injury and bruises. A heavy free weight held in the hand intended to exercise chest muscles may exert an unintentional heavy load on the knees. Free weights are also associated with dangers to other individuals exercising in the vicinity in case of loss of control. If a free weight falls from an individual's hand it may hurt other individuals.
Some exercise machines have been developed to overcome disadvantages associated with free weights and permit safe exercising. These exercise machines involve the use of adjustable weights loads enclosed in a frame, which are connected through pulleys, gears and cables to frames and handles. The user exerts force on the handles and frames, and the cables transmit the load of the weight to the user. This may reduce some of the dangers associated with free weights.
However, these exercise machines are expensive. Many of them are directed to exercising specific muscle groups. Further, these machines often have a limited adjustability and the configuration of use is largely fixed. It is difficult to use the same machine in different configurations. A machine devised for a healthy individual exercising in a gym may not be suitable for a hospitalized individual who is unable to move from his or her bed. A machine devised for exercising the thighs may not be useful for exercising the forearms.
The motion of free weights or the weights in exercise machines move according to the laws of gravity. When these weights are moved along a trajectory, they always exert a force component in a downwards direction. When a free weight is lifted, the part of the trajectory in which the weight is moved against the ground is controlled by the individual. However, in the final part of the trajectory, the weight moves towards the ground. In this part of the trajectory, the force exerted at every point of the trajectory against the user's muscles is uniform and dictated by the weight. In case of the exercise machines the force exerted is always uniform and depends on the selected weight or load.
This makes maintaining a uniform velocity throughout the trajectory very difficult for individuals. An individual may be able to move the weight with a controlled velocity for a part of the trajectory but may lose control, leading to a rapid velocity change. Such unintended velocity changes along the trajectory of motion of free weights or weights in exercising machines can cause short-term or long-term injuries to the user.
Certain exercises need the velocity of motion along the trajectory and exerted force to vary in a predetermined manner along the trajectory path of motion of the exercise equipment.
A need exists for a low-cost and flexible exercise machine that allows controlled motion exercise of various different muscle groups. A need also exists for an exercise machine that ensures the safety of the exercising individual and the safety of other individuals in the vicinity of the exercising individual. A need also exists for a machine that can be used by users who may not have full control over their bodies. A need also exists for an exercise machine that can be used by users in various positions such as standing, sitting or lying horizontally. A need also exists for a machine that exerts force varying along the trajectory of motion of exercise in a predetermined manner. A need also exists for a machine that allows exercising parts to move along a specified trajectory with a velocity that varies along the trajectory of motion in a predetermined manner. Various aspects and embodiments of the present invention are intended to address one or more of these needs.